Email Deliverability: Why Your Emails Land in Spam

Email deliverability is whether a message you send actually reaches the recipient's inbox instead of their spam folder or the promotions tab. When deliverability drops, the usual first guess is bad subject lines or the wrong send time. In most cases the real problem sits underneath the content: missing authentication records, a contact list full of dead addresses, or a sending pattern that looks automated to the receiving mail server.

This matters because a campaign with strong copy and a broken sender reputation still fails. Gmail, Outlook, and Yahoo decide where a message lands before a single human reads the subject line. Fix the mechanics first, then the copy has a chance to work. None of the fixes below require switching email platforms or rewriting your content — they are DNS records, list decisions, and a change to how you ramp up sending volume after a gap.

What causes emails to land in spam?

Inbox providers score every incoming message against a mix of signals: whether the sending domain is authenticated, how many recipients marked past messages as spam, how many addresses bounced, and whether the sending volume or pattern changed suddenly. A single bad signal rarely tanks deliverability. A combination does.

The most common combination in a small business account is an unauthenticated sending domain paired with a list that has not been cleaned in a year or more. Neither problem is visible from the inside — the sender sees "sent," not "filtered."

• No SPF, DKIM, or DMARC record on the sending domain
• A list with a high share of addresses that have not opened anything in 6+ months
• A sudden jump in send volume from a domain with no sending history
• Content that trips spam filters: excessive links, shortened URLs, or all-caps subject lines
• Sending from a free address (like a Gmail account) instead of the business's own domain

How do SPF, DKIM, and DMARC work together?

These three DNS records are how a receiving mail server confirms a message actually came from the domain it claims to. Without them, a mailbox provider has no reliable way to tell a legitimate sender from someone spoofing that domain, so it defaults to caution.

Google's guidelines for bulk senders lay out the authentication threshold mailbox providers now expect before mail is trusted by default (Google's sender guidelines). A domain missing any one of the three records is sending on trust alone, and trust alone is what filters exist to override.

What does a deliverability cleanup actually involve?

A cleanup is mechanical, not creative. It follows the same order every time because each step depends on the one before it.

1. Confirm SPF, DKIM, and DMARC are published and passing for the sending domain, not just for the marketing platform's default settings
2. Remove or suppress addresses that have not opened a message in the last 6 to 12 months
3. Remove hard bounces immediately and never re-add them
4. Check the domain's sender reputation with a tool like Google Postmaster Tools
5. Send a small re-engagement message to the list before resuming full-volume sends
6. Ramp volume back up gradually rather than returning to the old send size in one batch

Skipping the ramp-up step is the most common mistake. A domain that has been sending 500 emails a week and suddenly sends 5,000 looks like a compromised account to a filter, authentication records or not.

What if the sending domain is brand new?

A domain with no sending history has no reputation yet, good or bad, and mailbox providers treat that as a reason for caution rather than a clean slate. New domains need a deliberate warm-up period before they can send at full volume.

Start by sending small batches, a few hundred messages at most, to your most engaged contacts: people who have bought from you or opened recent messages from a previous address. Increase volume gradually over two to four weeks rather than announcing a launch to the full list on day one. A domain that earns a handful of opens and replies early on builds the reputation signal that lets it send larger volumes later without tripping filters.

Why does list hygiene matter more than people think?

A mailing list is not an asset just because it has a lot of addresses on it. An inbox provider tracks engagement per domain, and a list where most recipients never open anything drags down the reputation of every message that domain sends, including the ones going to people who do read them.

Removing inactive addresses feels like throwing away reach. It is closer to removing dead weight that was making every other message land worse. A smaller, engaged list consistently outperforms a larger, stale one on open rate, click rate, and inbox placement.

How often should you check deliverability?

Monthly, at minimum, and after any change to sending volume, platform, or domain. Authentication records do not expire, but sender reputation is a rolling average — a bad week can suppress placement for the following month even after the underlying issue is fixed.

The businesses that catch problems early are the ones checking bounce rate and spam-complaint rate as a routine, not the ones waiting for someone to say "I never got your email." By the time a customer says that, the damage to the domain's reputation is already a few weeks old.

When does it make sense to hand this off?

Checking DNS records once is a one-time task. Watching sender reputation, bounce rate, and list health every month is ongoing work that competes with everything else running a small business. That is the point where many businesses fold deliverability monitoring into whoever already manages their email marketing, so it gets checked on a schedule instead of after a complaint.

If your team already uses an email service provider like Mailchimp or Klaviyo, it is reasonable to assume authentication and list hygiene are handled automatically. They are not. The platform sends the message; the domain owner is still responsible for the DNS records and for deciding when to prune the list. An ESP will not stop you from mailing a stale list into a spam folder, and its default settings will not warm up a new sending domain for you.

The most common reason business owners put this off is that nothing looks broken from the inside. Sent mail shows as sent, campaign reports show a send count, and the drop only becomes visible once someone mentions they never got an email you sent weeks ago. By then the reputation damage already happened quietly, one filtered message at a time, which is exactly why this works better as a routine check than a reaction to a complaint.

Budgeting for ongoing marketing work, including things like this, is worth planning against real numbers rather than guessing — see our marketing budget guide for how to size it.

What to check this week

Start with the DNS records: confirm SPF, DKIM, and DMARC are published for your sending domain and that they are set to enforce, not just monitor. Then pull your last 90 days of bounce and complaint data from whatever platform you send through. Those two checks catch the majority of deliverability problems before they cost you a campaign.

If you want a second set of eyes on the setup, our marketing services page outlines how we handle this alongside broader campaign work, and you can reach out with your sending domain if you want a straight answer on where your authentication chain currently stands.